The production of natural gas and crude petroleum is carried out with a broad range of techniques generally involving any of a variety of pumping systems or non-pumping, "gas lifting" techniques. With the latter techniques, wells are produced on a periodic basis such that gas pressures, whether artificially or naturally induced, are permitted to build at the well as liquid accumulates therein. These liquids, which in most cases will include oil and salt water, are expelled by pressurized natural gas as the well is opened. The resultant "slug" of expelled liquid is directed into separation and collection facilities, separated gas conventionally being directed to a "sales" line for distribution by a utility. Achieving optimum production from a well requires an evaluation of many operational parameters such as casing pressure, tubing pressure, line pressure, as well as trends which those parameters exhibit over several periods of production. Production histories of the wells generally are unique, no two wells exhibiting the same performance characteristics or "signatures" and those signatures are seen to vary as the wells age. Failure to properly evaluate these well characteristics and control accordingly, may result in a "loading up" condition wherein liquids over-accumulate in the well to exhibit static pressure levels beyond the energy capabilities of the natural gas production reservoir which may be available to effect their removal. Such failures may be quite expensive to correct.
In the past, a procedure called "intermitting" was employed to produce a well wherein a mechanical clock controller, operating in a limited but repeating time cycle, periodically opened and closed the well. To aid the operator in devising the on-off schedule for a well, typically 7-day, two pen recorder charts were then and are now employed to record casing pressure and tubing pressure such that the operator could observe any pertinent trends upon visiting the well head. The mechanical controller long used for intermitting procedures had many drawbacks. It required frequent winding and thus often was neglected during adverse weather conditions as well as when located at remote and difficult-to-access well locations. Such crude, purely timed production techniques additionally limited the operator's capability for achieving a more optimal control.
Production control approaches have been taken by major oil producers which employ elaborate parameter monitoring coupled with equally elaborate communications which achieved a control dialogue with a centralized computer control facility. The economics associated with such network controls necessitated their use with large oil pockets, for example those encompassing more than 100 wells. For such installations, the communications links extend, for example, over distances as lengthy as 100 miles. Experience with these elaborate control systems has witnessed the vulnerability of elaborate communication systems to break-down as well as the down time propensities of computers. These problems have lead to a further need for "stand-alone" systems which will maintain an acceptable well operation in the presence of loss of centralized controls.
Smaller, independent well operators cannot afford the above-noted elaborate and expensive centralized control approaches as well as the important supporting technical personnel required for them. Generally, the independent operator must work with those untrained in the technical sphere and, thus, control equipment must be readily understood, reliable and simple. However, the smaller entities have improved well head control by resort to improved stand alone controllers coupled with each well head. For example, an electronic controller capable of operating over extended time periods under battery power was successfully introduced to the industry under the trade designation "DIGITROL". Described in U.S. Pat. No. 4,150,721 by W. L. Norwood, this controller provides not only a simplified control adjustment procedure but, importantly, a time cycle interruption feature accommodating conditions where the cyclical timing system should be overriden and subsequently reinitiated on an automatic basis.
These improved performance capabilities of the pioneer electronic controller later were considerably expanded with the introduction of a microprocessor driven programmable controller described in U.S. Pat. Nos. 4,352,376 and 4,532,052 by Norwood. With the logic capabilities of the microprocessor, the latter controllers are capable of significantly expanded combinational logic performance for tailored control over a given well head. However, these devices were called upon in many instances for specialized performance for given well heads, a requirement calling for recompiling programs and the like, a task generally found to be beyond the capacities of smaller independent operators.
A need exists for a stand alone controller which is readily programmable to meet an extended range of control conditions and which additionally contributes the function of the two pen recorder chart to show data representing well performance as well as the trends of that performance over predetermined periods of time. Additionally, it is desirable that some form of networking be made available for the smaller independent operator such that remote well head installations which normally are difficult to access may be remotely communicated with by systems within the realm of practical economics.
Very often to improve the production capabilities of a well, the tubing strings therein incorporate a plunger lift device. With such devices, when the well is shut in, the plunger is situated in the lowermost portion of the tubing string. As natural gas pressure develops within the well during this shut-in interval, the slug of liquid accumulates in the tubing string above the plunger. At an optimum point in time, the well is opened via a motor valve assembly coupled to the tubing string and a surge of pressure occurs functioning to move the slug of liquids into the separation and collection facilities and the gas cap into the sales line of the buyer. While the surge pressure involved in plunger lift is helpful in terms of fluid expulsion, the pressure surges are considered detrimental by gas purchasers, orifice meters and the like being driven off chart without some form of protection. To accommodate for the needs of the gas buyer, operators often will avoid plunger lift procedures or curtail full production through the employment of chokes and the like to restrict this pressure surge of capped gas. Gas-oil markets also influence techniques of production. In some cases, the market for this product is curtailed and it is desirable to shut-in or close the wells for an extended period, for example three weeks. Opening the wells following this interval may result in similar forms of high pressure surges which are detrimental to the system.